The invention relates to a method for treating and/or coating a surface of an object, especially a surface of a substrate, such as a semiconductor component or solar cell, wherein the surface is supplied with a gas that contains particles that will interact with the surface. The invention further relates to a device for coating and/or treating a surface of an object, such as a substrate, by supplying said substrate with a gas that contains particles for coating and/or treatment, with the device comprising a chamber that is formed by a top panel, a base panel and side panels of the surface to be coated and/or treated, and a longitudinal boundary panel that extends parallel or approximately parallel to said surface; the device further comprises a gas intake and a gas outlet port, and at least one heat source for heating the surface.
In coating substrates and/or surfaces via a CVD process (chemical vapor deposition), various principles of application may be used. It is possible, for instance, to direct the gas flow parallel to the surface of the substrate. In this, the substrate may be fixed or in motion. Directing the gas along the surface of the substrate creates a tendency toward a rapid depletion of the carrier gas. Furthermore, if the substrate is fixed, inhomogeneous deposition rates, inhomogeneous coating thicknesses, and uneven doping in the direction of the thickness and surface of the coating may result.
If the substrate is in motion, although a homogeneous coating thickness can be achieved, the deposition rate will be inhomogeneous. An uneven doping in the direction of coating thickness may also result.
In plug flow reactors, the gas that is to be supplied to a substrate surface flows perpendicular from above toward the surface that is to be coated. If the surfaces of the substrate are small, a homogeneous deposition rate can be achieved. Coating thickness and doping in the direction of the thickness and the surface of the coating are also homogeneous. However, if larger surfaces are to be coated, recycling the reactive gas becomes problematic, hence in plug flow reactors, positive results can be achieved only with relatively small substrate surfaces.
To produce homogeneous deposits over large surfaces, pancake reactors, which are similar in principle to the plug flow reactor, are used. In a pancake reactor, the surface to be coated is acted upon by the gas in a vertical position. The substrate itself is placed on a hot susceptor; the convection in the gas atmosphere that this creates results in a thorough mixing and homogenization of the gas. Accordingly, homogeneous deposition rates, homogeneous coating thicknesses, and homogeneous doping in the direction of the coating thickness and the coating surface are thus achieved. Homogeneity can be further increased by rotating the susceptor during the coating process. Even if such a coating process is suitable for use on large surfaces, and creates reproducible, high-quality epitaxial coatings, it must still be considered a disadvantage that the gas is introduced from the center of the system through a boring in the plate-shaped susceptor, and thus remains limited in its application to wafer coating.
Corresponding methods and/or reactors that are used in application are found in the source US-Z: Chemical Vapor Deposition for Microelectronics, Arthur Sherman, Noyes Publications, USA, pp 31-39, 150-174.
The process of rotating the substrate being coated in order to achieve adequate homogeneity in terms of coating thickness is known in the art; this process allows the inhomogeneities to be worked out in an azimuthal direction. With CVD processes in the field of semiconductors, substrates are thus rotated or at least placed in motion. In this, rotation presupposes rotationally symmetrical substrates, substrate carriers, and/or susceptors with precisely defined shapes and a suitable mass distribution ratio.
In the techniques described above, used with a horizontal CVD reactor, a plug flow reactor, or a pancake reactor, the substrate is ordinarily placed on a susceptor, which is heated either inductively or via lamps. If the gas that will interact with the substrate—frequently referred to as nutrient gas—is above said substrate, then the deposition of the coating, and thus the quality of the coating, will be influenced by the convection of the gas caused by the heating of the substrate. In this, the convection may be quite turbulent and irregular. In addition, if the hot gas comes into contact with the cold gas flowing in, then condensation and/or nucleation may occur in the gas phase, which will create mist or powder. Powdery deposits on the coating, however, will produce defects in a growing CVD layer. Furthermore, particles can result in defects, which must be prevented, especially in semiconductor and solar technology.